Myopia causes the eye to elongate, which in turn stretches and thins the retina and the sclera of the eye. Accordingly a myopic eye has a longer axial length than the normal eye. Noticeably, the axial length can vary among individuals. In animal studies, one eye is induced to myopia and the other eye is used as the control. The difference of axial length between the induced myopic eye and the control eye can be used to indicate the severity of myopia. In addition, the change of difference of axial length can also be used as a readout to assess the therapeutic effect for anti-myopic treatment. The elongation of eyeball is considered the major underlying mechanism to cause myopia complications such as retinal detachment, macular degeneration. That also explains why the correction of refraction without preventing axial length elongation (such as eyeglasses) cannot prevent myopia complications.
The paired box 6 (PAX6) gene belongs to a highly conserved family of transcription factors containing the paired and homeobox DNA-binding domains. PAX6 is involved in the development of the central nervous system and the eye. It plays significant roles during the induction of lens and retina differentiation, and has been considered the master gene in eye development. In humans, mutations in PAX6 are associated with a variety of human ocular diseases including aniridia, foveal hypoplasia, presenile cataract, and aniridia-related keratopathy (reviewed by Tsonis and Fuentes). In addition to the biological plausibility, a genome-wide linkage study revealed a strong linkage of refractive error to the PAX6 locus. Accordingly, PAX6, has been proposed as a candidate gene for the development of myopia. A low level of PAX6 may be a risk factor for myopia.
MicroRNAs (miRNAs) are noncoding, single-stranded RNA molecules of about 21-23 nucleotides in length. In animals, a mature miRNA is complementary to the 3′ untranslated region (UTR) of one or more messenger RNAs (mRNAs). The annealing of a miRNA to its target mRNA causes an inhibition of protein translation, and/or cleavage of the mRNA. miRNAs can regulate cell growth, differentiation, and apoptosis.
Chen et al (Invest. Ophthalmol. Vis. Sci., 53:2732-2739, 2012) report that microRNA-328 (miR-328) may influence myopia development by mediating the PAX6 gene.